Evidence of silicon substrate effect on improved electrolytic performance of Sb-SnO₂ thin films/polycrystalline Si/chromate solution structure

The photo-electrochemical properties of pure SnO2 and Sb-doped SnO2 grown on Si substrate (Sb(%)/SnO2/Si) thin films synthesized by the Atmospheric Pressure Chemical Vapor Deposition (APCVD) were studied. The nature of the substrate and its chemical composition were assessed. SnO2 and Sb(%)/SnO2/Si films crystallize in a tetragonal rutile-structure and the Sb-doping does not affect the growth direction of the diffracted peaks but increases the crystallites size. The lower Sb/Sn ratio (similar to 0.2) revealed a better homogeneity of SnO2 onto Silicon than the glass substrate. Indeed, the AFM images showed that Si gives a smoother Sb/SnO2 film. The electrochemical measurements were studied with the variation of Sb(%)/SnO2/Si. The Capacitance-Potential (C-2 - E) characteristics confirmed the n-type nature induced by the compensation mechanism Sb5+/Sn4+, the flat band potentials of -0.83 and -0.85 V for SnO2/Si and Sb(0.85 %)/SnO2/Si respectively were obtained and both values are cathodic enough to reduce Cr(VI). The variation of the impedance with the frequency and the effect of the substrate on the transport properties showed that the grain boundaries dominate the conduction mechanism, influenced by the microstructures of the films (crystallography and texture). Sb(%)/SnO2/Si/Cr(VI) solution provided variable electrochemical properties, and an appreciable difference in the light absorbance confirmed the chromate reduction (lambda(max) = 350 nm, 16 ppm) to less hazardous form Cr3+; a conversion of 80 % was obtained under solar light.